It is known that kite sails are made up of one or more soft sails, generally elliptical or semi-elliptical in shape, flat or semi-flat, where the concave side is designed to be placed in the wind to create a means of traction, and possibly movement, by a user or other, connected to the sail by cables called lines.
Such sails have many possible applications, particularly in sports involving sliding on land, water or snow, and used, for instance for kitesurfing, mountain boarding, snowkiting, kite buggying, all of which are powered by a traction kite. These sails are used to power all kinds of nautical or land equipment, sliding or rolling, but are also used in electricity generation systems that use the force generated by such sails.
Such a sail generally comprises a leading edge (front) and a trailing edge (rear).
The sail further comprises:                two lines that manage steering and power, known as rear lines, connected to the left and right-hand side rear ends of the sail;        two lines known as front lines, connected to the leading edge of the sail;        a fifth line known as the safety line, connected to the user by a dropping system and fixed directly or indirectly via optional bridling to the leading edge of the sail or one of the four front and rear lines.        
The ends of the four rear and front lines opposite the sail are connected to the user through a control bar; more precisely, the ends of the two front lines are connected to a central end going through the bar, while the ends of the rear lines are fixed to the left and right ends of the bar.
The central part of the bar is connected to the user by a dropping system connected to a harness worn by the user or the like. The bar is held by the user in their two hands.
Depending on the wind force, the user adjusts the traction power of the sail by varying its inclination along a variable plane demarcated by the fastening points of the front and rear lines, by shortening or lengthening the distance between the fastening point and the harness.
Depending on the wind force, the user can vary the traction power of the sail by varying its inclination using the sliding bar connected to the rear lines (steering and power) in relation to the front lines (traction).
If the wind force is too high or not high enough for the user, the user can also adjust the power of the sail and thus extend its range of use thanks to a central adjustment and deflection system that most generally connects the two front lines. That operation modifies the adjustment of the incidence of the sail.
In a known manner, this maneuver is carried out via a central adjustment and deflection system that most generally connects the two front lines centrally, and slides perpendicularly through or close to the bar. Said system makes it possible to adjust the incident inclination of the sail, by reducing or extending the distance between the rear trailing edge and the fastening point to the front harness. The same system or its equivalent may also be made from the rear lines.
Thus, by pushing or pulling the bar, the incidence of the sail can be decreased or increased, which decreases or increases the tension in the (front and rear) lines by aerodynamic effect.
To control the central deflection system, the user must release one hand, and the bar is then held in only one hand.
That creates a major drawback in terms of controlling the sail, which is all the more disadvantageous because the user precisely needs to better control the bar when the wind force and/or direction changes.
In the French patent application 1361291 filed by the applicant, a bar was proposed with a central winder on the bar that can be controlled by a single hand and associated with a deflection mechanism (internal to the bar) connected to the two ends of the rear cables.
Even though this system makes an advantageous improvement to prior bars, it can be improved in view of speed and responsiveness, the effort to be made by the user and the traction power on the cables.
Further, known mechanisms are not totally sealed, and the presence of sand affects their working and reliability.